From: Dan Connolly <connolly@w3.org>
Subject: DAML/RDF: a semantics and 2 more syntaxes
Date: Fri, 13 Oct 2000 16:17:13 -0500
> In response to a recent request for a semantics for DAML:
>
> [...]
>
> I'll share my my understanding of RDF semantics, and
> hence DAML semantics. Please understand that this
> is my own personal view of DAML/RDF; Jim H. has
> made it clear that DAML doesn't (yet) specify
> any one semantics, and lots of folks (including
> my co-authors!) have disagreed, in large or
> small part, with the position I take;
> to whit:
>
> [[[
> In [KIF] terminology, an RDF document is an atomic,
> simple, ground, knowledge base, restricted to
> 2-place predicates.
> ]]]
>
> -- section 6. A Logic built on RDF-NF
> of An Agent Markup Languagee version 0.5 draft
> http://www.w3.org/2000/07/DAML-0-5#Building
>
> To elaborate slightly: an RDF document is a serialization
> of a graph. To understand it, you parse the serialized
> form into a graph, and then consider each arc
> from s to o labelled p to be a KIF sentence (p s o);
> pretty much the same as a prolog fact p(s, o).
> p, s, o are URIs.
>
> In particular, I regard daml:equivalentTo as
> having the same semantics as (= X Y) in KIF.
> i.e.
>
> (defrelation http://www.daml.org/2000/10/daml-ont#equivalentTo (?x ?y)
> := (= ?x ?y) )
OK, this is a potential specification of the meaning of equivalentTo via
translation into some second-order logic. Under this specification,
it appears that equivalentTo would allow making equivalences between
unrelated logical statements.
However, the translation from daml into kif provided in the attachments to
your message doesn't carry this at all. In fact, I don't see ANY semantics
being provided by this translation (and I'm not sure that is was supposed
to, by the way). However, if it was intended that the translation into KIF
syntax was not intended to provide some help for semantics, then I don't
know what it was intended to be.
> The recent suggestion[026] that defined classes can be
> expressed without quoting/reification seems to
> suggest that DAML consumers be allowed to
> rely on information from the XML serialization about
> which properties were stated where. If you
> want to use RDF APIs and tools, that won't work.
> This information disappears when an RDF document is
> parsed into a graph.
I don't see this at all.
Again, let me reiterate my plea. What I want is some clear idea of what
the meaning of the DAML-ONT constructs are. I don't care too much about
how this meaning is conveyed, except that it be clear. (Of course, I do
happen to think that some methods for conveying meaning are better than
others.) To go along with the meaning, I would also like to see what
restrictions are placed on the constructs (see the ongoing discussion of
the difference between these two with respect to equivalentTo).
Peter Patel-Schneider